"Testosterone therapy in any form -- gel, pills or injections -- does not appear to cause adverse cardiovascular effects," said Dr. Pawan Patel, lead author of one of the studies and an academic physician at Regions Hospital in St. Paul, Minn.

The studies are to be presented next week at the American College of Cardiology (ACC) annual meeting, in San Diego. Research presented at medical meetings is typically viewed as preliminary until published in a peer-reviewed journal.

The two studies were released a day after the U.S. Food and Drug Administration issued a warning about the overuse of testosterone-boosting drugs by aging baby boomers trying to use hormone therapy to turn back the clock.

The FDA will require all prescription testosterone products to carry a warning label that cites a possible increased risk of heart attack and stroke, the agency announced Tuesday.

Patel said that, based on his research, "the FDA black box warning may be premature. We certainly need a long-term clinical trial before we put a black box warning on testosterone therapy."

Testosterone levels naturally wane as a man ages. Testosterone therapy is often used to treat the effects of low testosterone -- the "low T" cited in numerous ad campaigns. Diminished testosterone levels can have an effect on mood, memory, muscle mass, bone density and metabolism, the ACC said in a news release.

In the past five years, the use of testosterone replacement therapy has increased significantly, from 1.3 million patients in 2009 to 2.3 million patients in 2013, the FDA found. Nearly one in 25 men over the age of 60 receives testosterone therapy, the ACC said.

In its warning, the FDA reported that testosterone "is being used extensively in attempts to relieve symptoms in men who have low testosterone for no apparent reason other than aging. The benefits and safety of this use have not been established."

The FDA noted that some previous studies have "reported an increased risk of heart attack, stroke or death associated with testosterone treatment, while others did not."

As recently as 2013, a study of Veterans Administration patients revealed a 30 percent increased risk in heart attacks and strokes among men taking testosterone therapy, said Dr. Richard Becker, chief of cardiovascular health and disease at the University of Cincinnati College of Medicine.

"The risk was increased whether someone was known to have heart problems or not," said Becker, who's also director of the University of Cincinnati Heart, Lung and Vascular Institute.

Patel and his colleagues based their new findings on data from 29 previous studies on testosterone therapy, involving a total of nearly 123,000 men.

While the analysis revealed a 17 percent increased risk of heart-related disease associated with testosterone therapy, the risk was not statistically significant, the study authors said.

The second report was based on a community-based study from a Wisconsin health care system, in which researchers tracked health data from 7,245 men with low testosterone levels between 2011 and 2014. The data came from the electronic health records kept by 15 hospitals and 150 clinics in the Aurora Health Care system.

Researchers found no difference in heart attack, stroke and death between low-testosterone men who received testosterone therapy and those who did not, after adjusting for other risk factors.

"The reassurance we get from this analysis in the community setting is that testosterone replacement therapy in patients with low serum levels is not causing any harm, even if it is not providing much cardiovascular benefit [in this patient population]," study senior author Dr. Arshad Jahangir said in the ACC news release.

The findings "will help ease anxieties around this treatment and provide some information on which physicians can base their prescribing decisions," said Jahangir, director of the Center for Integrative Research on Cardiovascular Aging at Aurora Health Care.

The University of Cincinnati's Becker asserted that neither study should be taken as definitive proof that testosterone therapy is safe for heart health.

For example, Patel's research did find an increased risk for heart-related disease, even though that risk was not statistically significant. "Clinically, if your risk is increased by 17 percent, that might be important," Becker said.

There also are concerns that testosterone therapy might speed the progression of prostate cancer in men, Becker said. Prostate tumors can feed on the male hormone testosterone, he said.

At this time, Becker said, testosterone therapy should be considered only for men displaying symptoms related to low testosterone levels. He added that even then, "the potential risks and benefits have to be weighed very, very carefully by a clinician."

Becker and Patel agreed that a large clinical trial is the only way to finally figure out whether testosterone therapy poses a risk to heart health.

"To get the best answer, we need long-term clinical trials to compare testosterone against placebo," Patel said.

SOURCES: Pawan Patel, M.D., academic physician at Regions Hospital, St. Paul, Minn.; Richard Becker, M.D., chief of cardiovascular health and disease, University of Cincinnati College of Medicine, and director of the University of Cincinnati Heart, Lung and Vascular Institute; March 14-16, 2015, presentations, American College of Cardiology annual meeting, San Diego